The present invention is directed to a flow control valve operable to automatically stop the flow of fluid into a storage tank when the level of fluid within the tank rises to a predetermined level to prevent overfilling of the tank. The valve of the present invention is especially well adapted for use with underground gasoline storage tanks.
Underground gasoline storage tanks utilized at gasoline service stations are provided with a fill pipe which extends upwardly from the top of the tank to an inlet end located in a manhole in the service station apron. These tanks are filled from tank trucks by means of a large diameter hose which is sealingly coupled to the upper end of the fill pipe during the filling operation. Because of the relatively large capacity of the underground storage tanks--from 6,000 to 12,000 gallons--a relatively high flow rate during the filling operation is desirable and flow rates in the general range of 400 gpm are typical. At these high flow rates, it is quite common that the tank is overfilled and, upon uncoupling of the tank truck hose from the fill pipe, fuel within the hose spills into the manhole. As much as 35 gallons of fuel may be involved in such a spillage. To prevent this spillage from contaminating the soil, it is now required in many localities that the fill pipe be equipped with an overfill storage container, such as that disclosed in U.S. Pat. No. 4,793,387. However, prevention of overfilling of the tank is obviously the most desirable solution.
Monitoring of the fuel level within the tank during the filling operation presents a problem in that the sole access to the interior of the tank is via the fill pipe. Various sensing devices which will give a continuous reading of the fuel level within the tank during the filling operation have been proposed, however, typically these devices merely give a gauge reading to the fuel delivery man, who may not be paying close enough attention.
Various float actuated control arrangements have been proposed in the prior art in which a valve in the fill pipe inlet is shifted to a closed position by a float within the tank when the level of fuel within the tank elevates the float to a position at which the float causes the valve to close. U.S. Pat. No. 4,667,711 discloses various forms of such float controlled valves. As set forth in U.S. Pat. No. 4,667,711, one problem which confronts valves of this type is that of devising an arrangement which will enable the float and the mechanism coupling the float to the valve which will enable the float and its associated mechanism to be inserted into the storage tank through the storage tank fill pipe. In order to perform its function, when the float is in its operating position within the storage tank, it must be located at some position outside of the path of incoming fuel flow--i.e., offset from the fill pipe. A second problem, largely ignored by the prior art, including U.S. Pat. No. 4,667,711, is the water hammer effect produced by suddenly closing a valve in a flow passage through which fluid is flowing at rates in the order of 400 gpm. This problem is especially acute in the various forms of valves disclosed in U.S. Pat. No. 4,667,711 in that a valve plate is pivoted about a horizontal axis at one side of the flow passage, and upon actuation, the valve is shifted into the flow path and driven to its seat by the incoming flow.
A third problem presented by such float controlled valves is the fact that upon closure of the valve, the flow passage above the closed valve is filled with fuel which will spill when the tank truck hose is uncoupled from the fill pipe. This problem has been solved by overfill storage containers, such as that disclosed in U.S. Pat. No. 4,793,357. Excess fuel which spills into the overfilled container may be drained into the fill pipe, as by a manually actuated valve--see, for example, U.S. Pat. No. 4,793,357, assuming the float is so arranged as to actuate the valve when the storage tank is filled to about 95% of is capacity.
The present invention is directed to a float actuated valve assembly which is readily insertable into and removable from an existing underground storage tank fill pipe in a manner such that the float and associated valve actuating mechanisms are shielded from incoming fuel flow and in which water hammer effects generated by valve closure are minimized.